This invention relates to wavelength division multiplexers (WDMs) systems and, more particularly, to dense WDMs (DWDMs), in which dispersion compensation is utilized at both the receiver and transmitter ends, and further wherein a WDM is optimized overall.
Various effects of linear chromatic dispersion in optical communications systems have been investigated. In particular, the use of dispersion compensation techniques at either the receiver or transmitter ends of a wavelength division multiplexer have been of interest.
This invention pertains to the simultaneous use of dispersion compensation at both the receiver (RX) and transmitter (TX) ends of a dense WDM to obtain better performance. The invention provides techniques for optimizing dual dispersion compensation, given the characteristics of the overall WDM and its associated network.
One factor significantly affecting the optimum ratio for dispersion compensation at the RX and TX ends is the chirp value of the transmitter. Other factors include power level, number of channels, channel plan, fiber dispersion, and system length.
Providing dispersion compensation simultaneously at both the RX and TX ends of the WDM system can produce superior results compared with compensation at a single end. However, the type and distribution of the dispersion (dispersion ratio) between the RX and TX ends must be balanced for the particular system. If not properly balanced, the results can be inferior even to those for single ended compensation.
The dispersion compensation ratio can be adjusted experimentally by trial and error, but this method is burdensome and painstaking. Optimization can initially be more readily analyzed using a simulation, which describes the propagation of the light wave in the fiber. Software that can perform this analysis is available commercially. The analysis can simulate propagation along all channels and account for meaningful nonlinear effects and dispersion effects at the same time.
An article by Hayee, M. I., et al, I.E.E.E. Photonics Technology Letters, 1997, entitled, xe2x80x9cPre- and Post-Compensation of Dispersion and Nonlinearities in 10 Gb/s WDM Systemsxe2x80x9d, which is hereby incorporated by reference in its entirety, teaches that dual compensation gives the minimal penalty for each channel in dispersion-managed WDM systems. Further, the article teaches that the optimal amount of pre- and post-compensation is dependent upon the specific dispersion map used in the WDM system. Hayee describes a sparse system having only eight channels; and with power and distance which are appropriate only for low power (1500 km) submarine systems. Unlike the present invention, the pre- and post-compensation of dispersion set forth by Hayee are determined individually and not in a coordinated way, as befits a system.
In accordance with the present invention, there is provided a method and system for compensating dispersion in long haul broadband Dense Wavelength Division Multiplexers (DWDM systems). A typical long haul broadband DWDM in accordance with this invention, utilizes a system of DFB (distributed feedback) lasers comprising thirty-two channels on an ITU (International Telecommunications Union) grid. The lasers are multiplexed and modulated at 10 Gbit/s by a nominal zero-chirp modulator. The signals are directed to a system of five 90 km spans of large effective aperture fiber such as that sold under the registered trademark LEAF(copyright) by Corning Incorporated. Optical amplifiers provide signal gain at the input to each span. Commercial units of Dispersion Compensating Modules are provided. The dispersion compensating modules are applied at the transmitter and receiver ends. Proper selection of the distribution of total dispersion compensation determined by simulation, and verified by experiment, optimizes the DWDM system.
It is an object of this invention to provide an improved method and system for compensating dispersion and nonlinear penalties in long haul broadband Dense Wavelength Division Multiplexers (DWDMs).
It is another object of the invention to provide an improved method and system for compensating dispersions in long haul broadband DWDMs, in which dispersion compensation is utilized at both the receiver and transmitter ends, and further wherein the DWDM is optimized overall.